Method and apparatus for passively controlling airflow

ABSTRACT

A system and method for providing a substantially constant volume exhaust or ventilation air terminal system is shown for controlling exhaust and/or return airflow rates in a system having a central fan or ventilator. The system and method permits zone-by-zone or area-by-area airflow regulation or control in non-demand areas in response to a demand or call for ventilation in demand areas. In one embodiment, the system employs at least one constant airflow controller or regulator situated in a damper. Another embodiment shows a combination of a first constant airflow controller or regulator situated or mounted on a damper with a second constant airflow controller or regulator situated in a duct associated with the damper. In still another embodiment, a constant airflow controller or regulator is provided in a duct, and used in combination with a solid damper.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for controlling airflowand, more particularly, a method and apparatus for controlling airdistribution in fan assisted central exhaust and/or return airventilating systems.

2. Description of the Related Art

Generally, central ventilation fans and ventilators used for the purposeof removing or exhausting air from areas in a building or structure,such as bathrooms, utility closets, kitchens in homes, offices, andother areas, will simultaneously remove air from fixed inlet terminalsconnected to the central ventilation fan whenever the fan is operating.Whether the fan operates intermittently or continuously, this results inexcessive energy consumption as a result of removing heated andconditioned air from spaces that may not require ventilation simplybecause the demand for ventilation exists in one or more of the areas.

Previous attempts to limit a central fan or ventilation system toventilating only occupied areas by opening and closing terminal devices,caused fluctuations in duct air pressure, and ultimately caused a shiftin the amount of air removed or delivered to one or more of the areas orzones. This resulted in excessive ventilation rates and excessive energyusage in some areas and under-ventilating other areas, which in turn,caused poor indoor air quality related problems and a failure to meetminimum building code requirements in some instances.

Controlling the central fan speed or revolution per minute (RPM) toprevent the over or under-ventilation problem in zoned systems has beendifficult, expensive and generally ineffective in the past. The typicalfan control method involved monitoring either main duct pressure or thenumber of open zones to determine the total amount of airflow needed.However, a problem remained in that controlling the total system airflowdoes not ensure proper and/or constant airflow amounts at each zonebranched duct.

Moreover, controlling airflow rates at each zone or branched duct in asupply air system has been accomplished using variable air volume (VAV)terminals. These VAV terminals were designed to vary the airflow ratesin response to temperature needs. While VAV terminals have thecapability to control airflow at constant levels, they typicallyutilized an electrically or pneumatically powered control device thatmonitors duct pressure through a pitot tube and sends a signal to aseparate zone damper. These control devices required a separate powersource, separate parts, and direct coupling to, among other things, adamper actuator to allow for responsive zoned airflow control. If theVAV control device loses power, it will also lose it ability to controlairflow.

What is needed, therefore, is a system and method for controlling airdistribution in both fan assisted central exhaust systems and/or returnair ventilating systems that facilitates overcoming one or more of theproblems of the prior art.

SUMMARY OF THE INVENTION

It is therefore an object of one embodiment of the invention to providea ventilation terminal system and device with an integral primary zonecontrolled damper that regulates airflow in response to a switch,dehumidistat, light sensor, motion sensor, CO² sensor or the like.

An object of another embodiment is to provide a ventilation terminaldevice and system with a pressure independent flow control device thatis integral to the primary flow control, which in one embodiment may bea damper.

Another object of another embodiment of the invention is to provide aflow control device and system that regulates airflow to substantiallyconstant levels when exposed to varying duct pressures.

Still another object of another embodiment of the invention is toprovide a flow control device and system that is mechanically removedfrom an airflow stream when the primary control device is caused topermit airflow to a predetermined demand level.

Still another object of another embodiment of the invention is toprovide a control device for situating in an airflow stream to regulateor control airflow to a substantially constant or predetermined maximumrate.

Yet another object of another embodiment is to provide a system andmethod having a first control device that controls or regulates flow toa first substantially constant or predetermined rate, while another flowcontrol device controls or regulates flow to a second predeterminedlevel or rate.

Still another object of another embodiment of the invention is toprovide at least one or a plurality of flow control devices that requireno direct electric or pneumatic power source, but rather, utilize onlysystem duct pressure to regulate airflow to first and/or secondpredetermined levels, respectively.

Still another object of another embodiment of the invention is toprovide a minimum flow control device that will continue to operate if aprimary flow control device cannot be actuated to permit increasingairflow or it loses power.

Still another object of another embodiment of the invention is toprovide a ventilation control assembly and system that can be easilymaintained and/or removed from a terminal housing without disconnectingthe terminal to which the assembly is attached from any duct orventilation shaft.

Still another object of another embodiment of the invention is toprovide a system that is small enough to be mounted between floor,and/or ceiling assemblies, such as assemblies constructed of nominal 10″joists on 16″ centers.

Another object of another embodiment of the invention is to provide anassembly that utilizes a damper drive-motor powered by 120 volt, 24volt, 12 volt, or 220 volt AC or other suitable electrical voltagesupply.

Yet another object of another embodiment of the invention is to providea device that reduces or eliminates the need for routine maintenance ofthe type that is required by mechanical or electrical systems of thepast.

Still another object of another embodiment of the invention is toprovide a device that can be easily mounted in a fire or non-fire ratedceiling or wall assembly.

Yet another object of another embodiment of the invention is to providea device that will reduce the necessary central fan horsepowerrequirements and will facilitate saving on energy consumption byreducing the overall fan or ventilator requirements in the system.

In one aspect, an embodiment of the invention comprises a zone controlexhaust terminal comprising a housing having a first opening coupled toa duct and a second opening associated with an area to be ventilated,the housing directing airflow from the inlet to the outlet along apredetermined path and a damper hingeably coupled to the housing forcontrolling airflow between the area and a fan or ventilator, a motorfor driving the damper from a closed position at which the damperbecomes situated in the predetermined path and an open position at whichthe damper permits airflow along the predetermined path in response to amotor control signal and an airflow regulator situated in thepredetermined path, the airflow regulator regulating airflow along thepredetermined path when the damper is in the closed position.

In another aspect, another embodiment of the invention comprises a zonecontrol ventilation system for use in a building having a plurality ofareas to be ventilated, the system comprising at least one fan unit forgenerating airflow, a plurality of ducts coupled to at least one fanunit; a plurality of zone control exhaust terminals coupled to each ofthe plurality of ducts, respectively, and operatively associated witheach of the plurality of areas each of the plurality of zone controlexhaust terminals comprising a housing having an inlet coupled to a ductand an outlet associated with at least one of the plurality of areas tobe ventilated, a damper pivotally coupled to the housing, a motor fordriving the damper between a closed position and an open position atwhich the damper permits airflow between at least one fan unit and atleast one plurality of areas and into at least one of the plurality ofareas to be ventilated in response to a motor control signal, and anairflow regulator situated in an airflow path, the airflow regulator forregulating an airflow rate along the airflow path between the room andat least one fan unit.

In another aspect, another embodiment of the invention comprises amethod for maintaining a substantially constant airflow in a ventilationsystem having a plurality of ducts, the method comprising the steps ofpassively regulating airflow at a first rate through the plurality ofducts and causing airflow through at least one of the plurality of ductsat a second rate in response to a demand signal as the airflow throughthe other of the plurality of ducts continues to flow at the first rate.

In yet another aspect, another embodiment of the invention comprises amethod for controlling airflow through a plurality of ducts coupled to aventilator, comprising the steps of permitting airflow from theventilator through at least one of the plurality of ducts at asubstantially constant rate and permitting airflow through at least oneof the plurality of ducts to an area at a demand rate that is greaterthan the substantially constant rate in response to a demand signal.

In still another aspect, another embodiment of the invention comprises amethod for providing zone-by-zone airflow regulation for regulatingairflow to substantially constant levels, comprising the steps ofcontrolling airflow substantially constant through a plurality ofterminals associated with areas where no ventilation airflow is demandedat a first rate and controlling airflow through said terminal at asecond rate, which is higher than said first rate in areas whereventilation airflow is demanded in response to an airflow demand at ademand rate.

In yet another aspect, another embodiment of the invention is to providea method for regulating airflow to a plurality of zones of a buildinghaving a fan, comprising the steps of situating a primary regulator inoperative relationship with each of said plurality of zones to regulateairflow between each of said plurality of zones and said fan andsituating at least one constant airflow regulator in operativerelationship with each of said primary regulators in order to regulateairflow between each of said plurality of zones and said fan such thatwhen said primary regulator permits a demand airflow between one of saidplurality of zones and said fan, said at least one constant airflowregulators control or regulate airflow such that airflow to at least theother of said plurality of zones is substantially constant.

In still another aspect, another embodiment of the invention is toprovide a method for regulating airflow to a substantially constantlevel in each of a plurality of zones in a structure, said structurecomprising an airflow generator and at least one conduit for providingfluid communication between each of said plurality of zones and saidairflow generator and said method comprising the steps of causingairflow to a demand level in any of said plurality of zones whereairflow to said demand level is demanded and regulating airflow to asubstantially constant level in the other of said plurality of zoneswhere airflow to a demand level is not demanded.

In yet another aspect, another embodiment of the invention comprises asystem for regulating airflow in a structure having a plurality of zonesand said system comprising an airflow generator and a plurality ofterminals associated with each of said plurality of zones, respectivelya conduit for coupling said airflow generator to each of said pluralityof terminals a plurality of primary regulators coupled to said pluralityof terminals, respectively, for causing airflow to a demand level in oneof said plurality of zones in response to a demand and a plurality offirst constant airflow regulators situated between each of saidplurality of zones, respectively, and said airflow generator to regulateairflow between said airflow generator and those other plurality ofzones where demand airflow is not demanded to a first predeterminedlevel.

In another aspect, another embodiment comprises a damper assembly foruse in a ventilation system having an airflow generator, a terminalassociated with an area to be ventilated, and a duct for coupling theairflow generator to the terminal, the damper assembly comprising: asupport, a damper pivotally coupled to one support, a motor mounted onthe support for driving said damper between a closed position and anopen position and the damper assembly being detachably secured andremovable from the system without dismantling or disconnecting eitherthe duct or the terminal.

These are illustrative objects. Other objects and advantages of theinvention will be apparent from the following description, theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

FIG. 1 is a perspective view showing an embodiment of the invention,illustrating the use of a fan or ventilator in combination with acentral shaft in combination with one or more terminals associated witheach area or zone to be ventilated;

FIG. 2 is a fragmentary view of another embodiment of the inventionshowing a system utilizing a ventilator in combination with one or moreterminals;

FIG. 3 is a fragmentary view of a variable fan ventilation or exhaustsystem in accordance with one embodiment of the invention;

FIG. 4 is an exploded view of an embodiment illustrating, among otherthings, a housing, the ventilation duct, and a plurality of constant aircontrollers or regulators;

FIG. 5 is a fragmentary and sectional view illustrating various featuresof the embodiment shown in FIG. 4 and also illustrating a damper havingan aperture for receiving an airflow controller or regulator and alsoshowing the damper in phantom after the airflow controller or regulatorhas been received in the aperture and the damper has been actuated bythe drive motor to an open position;

FIG. 6 is an assembled view of the embodiments illustrated in FIGS. 4and 5;

FIGS. 7A-7B illustrate one embodiment of the invention and alsoillustrates a plurality of airflow versus pressure differencecharacteristic curves relative to the airflow in each of the ductsillustrated;

FIGS. 8A-8B is a view of another embodiment of the inventionillustrating a airflow controller or regulator situated in the damperand associated curves, but with no airflow controller or regulatorsituated in any of the ducts;

FIGS. 9A-9B illustrate another embodiment of the invention, illustratinga system having a plurality of solid dampers, each of which comprise anassociated constant airflow controller or regulator situated in a ductassociated with each damper;

FIGS. 10A-10B show various characteristic curves of a prior art constantairflow regulator and a prior art bulb-type controller or regulator(FIG. 10A) and a vain-type controller or regulator (FIG. 10B);

FIG. 11 illustrates the use of a terminal of the type shown in FIGS. 4and 5 mounted in a central pressurized shaft and further illustrating anopen duct associated with the housing of the terminal open to thepressure in the central shaft; and

FIGS. 12A-12B illustrate another embodiment of the invention wherevarious combinations of features of a primary, secondary, and tertiarycontrol or regulators may be used in various combinations, with theembodiment shown in FIGS. 12A-12B being a representative example.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to FIGS. 1-3, a zone control ventilation system or passiveflow control system 10 for use in the building 12, such as a multi-storycommercial building (FIG. 1), multi-story condominium or apartmentbuilding (FIG. 2), a residential building (FIG. 3). The system 10provides a system, apparatus and method for providing on-demand airflowat a demand airflow rate and a passive airflow at a passive airflow rateto a plurality of zones or areas 14 in the manner described laterherein.

The system 10 comprises at least one fan 16 (FIGS. 1 and 3), or thesystem 10 may comprise a ventilator 17, such as one or more of themulti-port ventilator series (“MPV”) model series MPV ventilatorprovided by American Aldes Ventilation Corporation of Sarasota, Fla. Itshould be understood that other suitable ventilators or fans may be usedand the invention is not limited by these particular model types.

The system 10 further comprises a plurality of ducts 18 that are coupleddirectly to the at least one fan 16 or ventilator 17, as illustrated inFIGS. 2 and 3, or coupled to a main ventilation duct or shaft 20 (FIGS.1 and 11) that is coupled to either the at least one fan 16 orventilator 17. The plurality of ducts 18 are each coupled to at leastone or a plurality of zone control exhaust terminals 22, at least one ofwhich is operatively associated with each of the areas 14 to beventilated. Although the embodiments illustrated in FIGS. 1-3 show asingle zone control exhaust terminal 22 associated with each of theareas 14, it should be understood that more than one of the plurality ofzone control exhaust terminals 22 may be associated with each of theareas 14. Although not shown, not every area or zone 14 in the building,structure or residence 12 must have one or more of the plurality of zonecontrol exhaust terminals 22, although in a preferred embodiment atleast one of the plurality of zone control exhaust terminals 22 isassociated with each area 14.

Also, while the illustration shown in FIG. 2 shows a multi-portventilator 17 coupled directly to each of the plurality of zone controlexhaust terminals 22 via ducts 18, the zone control exhaust terminals 22may be coupled directly to the main ventilation shaft 20 or to arteryducts, such as ducts 18 (FIG. 1), that extend from the main ventilationshaft 20. Alternatively, as illustrated in FIG. 11, the terminal 22 maybe situated interior of the shaft, with an open duct extension 30, whichin one embodiment is at least 22 inches. Note that the duct extension 30has an end 30 a coupled to the terminal 22 and an end 30 b that is opento the interior area 20 c of shaft 20. It should be understood that theinterior area 20 c of shaft 20 has an interior pressure created orprovided by the at least one fan 16 or ventilator 17.

Referring to FIGS. 4-6, various details of one of the plurality of zonecontrol exhaust terminals 22 will now be described. It should beunderstood that each of the plurality of zone exhaust terminals 22comprise substantially the same parts, although they do not have to beidentical to each other as will become apparent later herein. Each ofthe zone control exhaust terminals 22 comprises a box-shaped housing 24having a plurality of flanges 26 and 28. The flanges 26 and 28 providemeans for mounting the housing 24 to a structure, such as betweenadjacent 10″ joists or trusses on 16″ or 22″ centers in a ceiling orroof of the building 12 or between adjacent studs (not shown) in a wall29 (FIG. 1) of the building 12, or to a wall 23 (FIG. 11) of shaft 20.

As illustrated in FIGS. 4 and 6, the housing 24 is generally rectangularand comprises the duct extension or collar 30 for coupling the housing24 to duct 18 and for communicating with an opening 32 into an area 34defined by the housing 24. The duct collar 30 is conventionally coupledto the duct 18 as illustrated in FIG. 6. As mentioned earlier, however,terminal 22 could be mounted to shaft 20 and the end 30 b of duct collar30 could be open to the interior area 20 c of central shaft 20. Thehousing 24 further comprises a grille or cover 36 for covering a secondopening 38 of the housing 24. The second opening 38 is associated or incommunication with the area or zone 14.

The system 10 further comprises an air restrictor or damper assembly 40which will now be described relative to FIG. 5. The assembly 40comprises a generally U-shaped frame or housing 42 having an L-shapedbracket 44 welded or secured thereto. The apertures 46 and 48 typicallysupport and receive a drive shaft 50 which is coupled to and pivotallydriven by a motor 52 that is operatively coupled to a switch 54 asshown. The switch 54 may be a wall switch situated on, for example, thewall, such as a wall 29 in FIG. 1, associated with the area 14. Theswitch 54 may be a manual wall switch actuated by a user, or the motor52 may be coupled and respond to at least one of a motion sensor, manualcontrol, timer mechanism, light sensor, occupancy sensor, CO² sensor orother indicators or sensors of presence when a user enters or exits oneof the areas 14.

The generally U-shaped support, member bracket 42 is received in thearea 34 (FIG. 4) of housing 24 and secured between housing walls 24 aand 24 b with a plurality of screws 56 as shown. Note that the assembly40 further comprises a primary flow control, which in the illustrationis a damper 58 that is secured by a weld, screws or other suitable meansto the drive shaft 50 of motor 52. The damper 58 is pivotally driven bythe motor 52 in response to a user actuating the switch 54, for example,from an off position to an on position. It should be understood that themotor 52 is operatively coupled to a power sources an AC power source(not shown) in one embodiment, such as a 12V, 24V, 120V or 220V AC, buta DC power source may also be used. When the switch 54 is actuated by auser to the on position, the motor 52 becomes energized and pivotallydrives the damper 58 from the closed position to the open positionillustrated in phantom in FIG. 5.

It should be noted that the damper 58 is operatively associated with andsituated adjacent to an opening 32 (FIG. 4) in the wall 24 c of housing24. A first side 58 a of damper 58 may comprise a foam or other sealingmaterial secured thereto by an adhesive for sealing the damper againstthe surface 24 c of housing 24 when the damper 58 is in the closedposition illustrated in FIG. 6. Note that the assembly 40 comprises aspring or plurality of springs 70 that act upon a joining portion 42 bof the generally U-shaped support 42 and on the surface 58 b of damper58 to urge or bias the damper 58 in the direction of arrow A in FIG. 5so that the damper 58 is biased in the closed position illustrated inFIG. 6. The motor 52 retains the damper 58 in the open position duringany demand period, which is the period in time that the motor 52 isbeing activated.

In one embodiment shown in FIGS. 4, 5 and 9A-9B, the assembly 40 mayfurther comprise a switch 62 that is mounted on a flat area or ledge 42c of generally U-shaped bracket 42 as illustrated in FIGS. 4 and 5. Theswitch 62 is operatively coupled to the at least one exhaust fan 16 orventilator 17 such that when the damper 58 is actuated or driven fromthe closed position illustrated in FIG. 6 to the open position (shown inphantom in FIG. 5), a first side 58 a of damper 58 actuates the lever orswitch 62 coupled to the power source (not shown). When the switch 62 istriggered, the exhaust fan 16 or ventilator 17 becomes energized inresponse, thereby causing an increase of airflow in the ducts 18 orshaft 20. When the damper 58 returns to the closed position, forexample, when the user activates switch 54 to the off position, thedamper 58 in the embodiment shown FIGS. 9A and 9B is driven or actuatedto the closed position to close the opening 32 and release the switch 62to cause at least one fan 16 or ventilator 17 to turn off.

One feature and advantage of this design illustrated in FIGS. 4-5 isthat it is easy to perform maintenance on or remove the assembly 40after it is installed, although it is not believed that much maintenancewill be required.

Returning to FIGS. 9A-9B, an embodiment is illustrated where theventilator 17 or at least one fan 16 is only on when the user actuatesthe switch 54 to the on position. In contrast, the embodimentsillustrated in FIGS. 7A-7B and FIGS. 8A-8B, described later herein, doesnot utilize switch 62 to activate at least one fan 16 or ventilator 17.In these embodiments, at least one fan 16 or ventilator 17 provide aconstant airflow in the ducts 18, 19 or shaft 20. However, when a damper58 in the system 10 is opened in these illustrative embodiments, atleast one fan 16 or ventilator 17 responds to a decrease in duct systemresistance or demand for increased airflow and automatically causes anincrease in fan or ventilator speed, thereby causing a resultantincrease in the airflow in the shaft 20 and ducts 18 in response and ina manner conventionally known.

Referring to FIGS. 4-6, the assembly 40 further comprises at least oneor a plurality of airflow regulators 71 and 73 (FIG. 6) and/or 72 and 74(FIGS. 1-5). In one embodiment, the airflow regulators 71 and 73 areintegral constant dynamic airflow regulators, such as the constantairflow regulators CAR I and CAR II available from American AidesVentilation Corporation, 4537 Northgate Court, Sarasota, Fla.34234-2124. As illustrated in FIGS. 4 and 5, note that the damper 58comprises an aperture or opening 59 defined by the interior area asshown. The diameter of the interior wall 58 d in damper 58 isdimensioned to receive the airflow regulator 72 as shown. Asillustrated, bulb-type constant airflow regulators, such as thoseregulators 71 and 73 illustrated in FIG. 6, may be used and these arealso available from American Aides Ventilation Corporation.

It should be understood that the constant airflow regulators 72 and 74may comprise different specifications in a preferred embodiment and theyboth provide constant airflow regulation. For example, the constantairflow regulators 72 and 74 provide constant airflow regulation byoperation of the vane 72 a (FIG. 4), which acts to at least partiallyclose the opening 59 (FIG. 5) in a manner conventionally known. Incontrast, the constant airflow regulators 71 and 73 (FIG. 6) provideconstant airflow regulation by the inflating action of the constantairflow regulator bulb 71 a and 73 a, respectively, and in a manner thatis conventionally known. As illustrated in FIG. 6, note that the bulbs71 a and 73 a are generally hour-glass shaped. As a static pressureincreases in the ducts 18, the static pressure around the bulbs 71 a and73 a increases, thereby causing the bulbs 71 a and 73 a to inflate andthereby decreasing the area around the bulbs 71 a and 73 a. Atsubstantially the same time, as the static pressure around the bulbs 71a and 73 a increases, an air velocity also increases thereby resultingin constant airflow. The constant airflow regulators 71, 72, 73 and 74thereby provide a generally or substantially constant airflow regardlessof pressure differences in the system 10. FIGS. 10A and 10B graphicallyillustrate the operative characteristics of the airflow regulators 71,72, 73 and 74. It should be understood that the associatedspecifications will change depending upon the specifications selected bythe user. The operation of the system 10 will now be described relativeto several illustrative examples shown in FIGS. 7A-9B. For ease ofillustration, the embodiment of FIGS. 7A-7B will be illustrated or usedin the embodiment of FIG. 1, FIGS. 8A-8B will be illustrated as used inthe embodiment of FIG. 2, and FIGS. 9A-9B will be illustrated as used inthe embodiment of FIG. 3.

In the embodiments shown in FIGS. 7A-9B, the damper 58 provides primaryairflow regulation or control. The damper 58 is used in combination withat least one of either the first or second regulator 72 or 74 asillustrated in FIGS. 7A-9B. In embodiments shown in FIGS. 9A-9B, theconstant airflow regulator 74 permits a predetermined amount of airflowand provides substantially constant airflow regulation to apredetermined or maximum airflow rate. In contrast, the airflowregulator 72 in the illustration of FIGS. 8A-8B provides substantiallyconstant airflow regulation at a predetermined amount or a minimumamount of airflow. When the regulators 72 and 74 are used together asillustrated in FIGS. 7A-7B, they control or regulate airflow to both aminimum and maximum level, respectively, while the damper 58 controls orregulates airflow to a primary demand level, such as an airflow levelrequired to provide increased ventilation to a room in response to ademand signal from a user.

Typical airflow versus pressure difference characteristics aregraphically illustrated by the graphs under each terminal 22 in FIGS.7A-9B. It should be understood that the minimum amount of airflow rateand maximum of airflow rate will be dependent upon the size andspecifications of the airflow regulators 71, 72, 73, and 74,respectively, selected. The user's selection of the appropriate constantairflow regulator 71-74 will depend on the environment or application inwhich the system 10 is being used. In one illustrative embodiment shownin FIGS. 7A-7B, the minimum airflow rate may be on the order of at least10 cubic feet per minute (“CFM”) and the maximum amount of airflow ratemay be less than or equal to approximately 400 CFM, but this will bedifferent depending on the application.

Returning to FIG. 5, note that the damper 58 is comprised of a generallycircular planar member 58 b lying in a first plane P1 when the damper 58is in the closed position illustrated in FIG. 6. After the constantairflow regulator 72 is received in the area 59 defined by wall 58 d(FIG. 4) of the planar member 58 b, the constant airflow regulator 72lies in the first plane P1 or directly in the airflow path of airflowing into the opening 32 (FIG. 4) of housing 24. When the damper 58is in the closed position shown in FIGS. 5 and 6, the constant airflowregulator 72 regulates, permits or controls the airflow to the constantrate as dictated by the specifications for the constant airflowregulator 72 selected by the user. Thus, it should be understood thatwhen the damper 58 is actuated from the closed position to the openposition (illustrated in phantom in FIG. 5 and in the illustration ofFIGS. 7A-7B and 8A-8B), the airflow regulator 72 is removed from theairflow path, thereby removing the minimum or constant airflow regulatorfrom the opening 32 and from the airflow path between the area 14 andthe duct 18.

It should be understood that one or both of the constant airflowregulators 72 and 74 may be used in various combinations, such as theillustrative combinations that will now be described relative to FIGS.7A-9B. It should be understood that the illustrations in FIGS. 7A-9Bshow the damper assembly 40 (FIG. 4) and generally U-shaped member 42removed from the housing 24 for ease of illustration.

In the embodiment shown in FIGS. 7A-7B, the constant airflow regulator72 is situated in each damper 58 associated with each of the zones orareas 14. The constant airflow regulator 74 is situated in each duct 18as shown. In the illustration in FIGS. 7A-7B, the fan 16 runscontinuously at a first fan speed to provide constant ventilationairflow at a first rate. As illustrated in FIG. 7A, as air flows fromthe zones or areas 14 into the ducts 18, the air flows both through theconstant airflow regulator 72 and constant airflow regulator 74. Asexhaust air from fan 16, for example, is pulled from each zone or area14 through the duct 18, the constant airflow regulator 72 providesconstant airflow regulation to the first predetermined or minimum level.When there is a call or demand for increased ventilation in a remotearea 14, such as when the user in one area 14 actuates the switch 54 tothe on position as illustrated in FIG. 7B, the damper 58 in the demandarea 14 is driven by motor 52 to the open position. The fan 16 sensesthe demand and causes increase in speed to a second fan speed. Thedampers 58 in the other remote areas 14 remain closed, as shown by thetwo leftmost airflow regulators 72 shown in FIG. 7B. These regulators 72provide constant airflow control or regulation to the firstpredetermined or minimum level dictated by the specifications of thoseconstant airflow regulators 72. Notice that the increase in airflowthrough those constant airflow regulators 72 causes vanes 72 a (FIG. 4)to partially close as shown in FIG. 7B, thereby controlling orregulating airflow to the desired rate. Substantially simultaneously,notice in the right-hand portion of FIG. 7B that the constant airflowregulator 72 in the damper 58 has been actuated to the open position andremoved from the airflow path, thereby permitting increased airflow intoand through the duct 18 from the area 14 as shown. The second constantairflow regulator 74 controls or regulates airflow to the secondpredetermined maximum level, while the constant airflow regulators 72associated with the other zones or areas 14 control or regulate airflowto the first or minimum level.

Thus, the system 10 in the embodiments in FIGS. 7A-7B provides means forregulating or controlling airflow to the first predetermined or minimumflow rate in non-demand areas or zones 14 and between the firstpredetermined or minimum rate and the second predetermined or maximumrate during demand periods in demand zones or areas 14. In other words,the constant airflow regulator 72 in FIGS. 7A-7B facilitate controllingor regulating airflow to a substantially constant predetermined orminimum rate through each of the ducts 18. During ventilation demandperiods in those demand areas 14 where there is a demand for increasedventilation, such as when a user activates switch 54, the damper 58 hasbeen actuated to the open position. As illustrated by the rightmostassembly in FIG. 7B, at least one fan 16 or ventilator 17 responds tothe pressure drop and increases fan speed, causing increased airflow atthe increased or demand rate in response thereto. This causes increasedventilation from the area 14 where increased ventilation is demanded andthrough duct 18 and, ultimately, to the exhaust duct 19 associated withthe building 12. Substantially simultaneously, the constant airflowregulator 72 in the two leftmost ducts (when viewed from left to rightin FIG. 7B) regulate and control the airflow through the ducts 18 and sothat airflow continues at substantially the constant rate up to theminimum airflow rate which is dictated by the constant airflow regulator72 selected. The airflow in the system 10 is graphically illustrated bythe graph under each of the regulators 72 and 74.

When the damper 58 in FIGS. 7A-7B is closed, the constant airflowregulators 72 or 74 that have the lowest maximum airflow specificationwill limit or regulate the maximum airflow to that specification. Forexample, if the constant airflow regulator 72 in FIG. 7A permits amaximum 10 CFM, while constant airflow regulator 74 permits a maximumairflow of 50 CFM, the airflow will be regulated to 10 CFM in theillustration shown in FIG. 7A when the damper 58 is in the closedposition. When one of the dampers 58 in the system 10 is opened, theconstant airflow regulator 72, mounted in the damper, is removed fromthe airflow path into opening 32 (FIG. 4), thereby permitting airflow atgreater than 10 CFM. As the fan 16 or ventilator 17 cause airflow toincrease, the regulator 74 regulates airflow through the duct 18 up tothe maximum 50 CFM rate mentioned earlier. The airflow versus pressurecharacteristic is graphically illustrated by the graphs associated withthe dampers 58 shown in FIGS. 7A-7B.

Referring back to FIGS. 9A and 9B, another illustrative embodiment isshown. In this embodiment, the regulator 74 is situated in the duct 18,but regulator 72 is not in the damper 58. In this embodiment the damper58 and wall 58 b are solid and only regulator 74 is used. During normaloperation when there is no call or demand for ventilation or exhaust thedampers 58 are solid, remain closed and no ventilation through the ducts18, for example, is permitted. The fan 16 or ventilator 17 provideairflow or turn on in response to the user actuating switch 54 whichcauses motor 52 to drive damper 58 from the closed position to the openposition. When there is a call or demand for exhaust, the user activatesthe switch 54 and damper 58 activates switch 62, as described earlier,to turn on the fan 16 or ventilator 17 to cause an increased airflow toa demand rate. The airflow in the two leftmost ducts shown in FIG. 9Bare continued to be blocked by solid damper 58 in this embodiment. Therightmost open damper 58 in FIG. 9B is open, but regulator 74 controlsor regulates airflow to the second predetermined or maximum ratementioned earlier. The graphs associated with the dampers 58 illustratethe airflow versus pressure difference for this embodiment.

FIGS. 8A and 8B show another embodiment. In this illustration, theconstant airflow regulator 74 has been removed from the system 10. Theregulators 72 permit minimum flow rate into the ducts 18 when thedampers 58 are in the closed position. When one damper 58 is driven bymotor 52 to the open position, as illustrated by the rightmost damper 58in FIG. 8B, then unregulated airflow is permitted in the duct 18associated with the open damper 58. The constant airflow regulators 72in the other dampers 58 provide airflow control and regulation to thefirst predetermined or minimum level, as illustrated by the airflowversus pressure graphs in FIGS. 8A and 8B.

Comparing the embodiment of FIGS. 7A and 7B to the embodiment of FIGS.8A and 8B, notice that the constant airflow regulator 72 associated withthe rightmost duct 18 shown in FIG. 7B has been removed from the directairflow path between the zone area 14 into the duct 18, therebypermitting an increased airflow through the duct 18. The second constantairflow regulator 74 in FIG. 7B limits the maximum amount of airflowthrough the duct 18 to the second predetermined amount or the maximumrate specified by that constant airflow regulator 74. Substantiallysimultaneously, the constant airflow regulator 72 associated with thetwo leftmost ducts 18 (as viewed in FIG. 7B) in the areas or zones 14where ventilation is not demanded continue to limit the amount ofairflow to the minimum level amount. In this regard, notice that thevanes 72 a associated with the two leftmost ducts have closed slightly,thereby limiting the airflow to the specification of those constantairflow regulators 72.

In contrast, the embodiment in FIGS. 8A and 8B does not utilize theregulators 74. Therefore, air flows unregulated into and through theduct 18 associated with the damper 58 in the area or zone 14 whereventilation is demanded. No maximum airflow control or regulation isprovided in the duct 18 associated with that open damper 58.

Thus, it should be understood that the system 10 may be provided withone or more constant airflow regulators 72 and 74 in variouscombinations and arrangements with damper 58 that is solid or that has aregulator 72 mounted therein to regulate or control airflow to asubstantially constant minimum and/or maximum level in the areas 14. Ondemand, the damper 58 may be actuated from the closed to the openposition when the user desires to have increased airflow, such asventilation airflow, in the zone or area 14, such as a bathroom.

It should be understood that the regulators 71-74 and features of thevarious embodiments in FIGS. 7A-9B may be mixed or interchanged andprovided in a single system. One illustrative combination is shown inFIGS. 12A-12B. For example, a system 10 may have dampers 58 withregulators 71 or 72, with or without regulators 73 and 74. Some dampers58 may be provided with the solid planar member 58 b and without anopening 59 similar to the dampers in FIG. 9B, while other dampers 58 andregulators 72 and 74 may be provided as in the illustrations shown inFIGS. 7A-8B.

As mentioned earlier, it should be understood that while the system 10and method have been shown utilizing the switch 54 that may be actuatedby the user, other means for energizing and actuating the motor 52 todrive the damper 58 from the closed position to the open position may beused. For example, the system 10 may utilize any suitable means forproviding a motor control signal for controlling the motor 52, such asthe switch 54, a dehumidistat or occupancy sensor that senses when anoccupant has entered or left a room, a timer, a CO² sensor, or anycombination of the aforementioned means.

Advantageously, one feature of the embodiments illustrated is that itprovides ventilation airflow regulation or control from the zones orareas 14 through at least one or a plurality of the ducts 18 to amaximum airflow rate or less or between minimum and maximum airflowrates. Note that the step of permitting airflow from the fan 16 orventilator 17 is performed passively utilizing one or more of theconstant airflow regulators 72 or 74.

Advantageously, the aforementioned embodiments provide a primary flowcontroller or regulator in the form of the damper 58 and at least one ora plurality of other flow controllers or regulators, such as theconstant airflow regulators 71 and 72. These airflow regulators may beused alone or in combination with another constant airflow regulator 73or 74.

As mentioned earlier, one advantage of the embodiment of FIGS. 4-6 isthat maintenance is much improved over prior art systems because theassembly 40 can be completely removed from the housing 24 without havingto disconnect the housing 24 or terminal 22 from any ducts or shafts. Itshould also be understood that the constant airflow regulators 71-74require little or no routine maintenance, unlike the electrical andmechanical systems of the past.

The housing 24 does not have to be disconnected from the duct 18 if itis necessary to make any repairs or maintenance. The flow controldevice, such as regulators 72 and 74, require no direct electrical orpneumatic power source, and can regulate and control the airflow byutilizing only system duct pressure. Thus, even if there is no power toswitch 54 or motor 52, the regulators 72 and/or 74 will continue toregulate airflow.

Another feature of one embodiment is the small size of the terminal 22,which has dimensions of 10″×10″×8″. The terminal 22 is capable of beingmounted between floor, and ceiling assemblies, such as those constructedof standard joists on 16″ centers.

Because the system 10 is capable of regulating and controlling airflowin the various zones or areas 14 on an as needed basis, the overallcapacity requirements of the central fan 16 and/or ventilator 17 can bereduced because the system 10 is capable of providing constant airflowin non-demand areas 14 and airflow at a demand rate in those areas whereincreased airflow or ventilation is demanded. This enables a smaller fan16 or ventilator to be utilized in the system 10.

The system 10 advantageously provides a flow control device thatregulates airflow to constant levels when exposed to varying ductpressure.

While the method herein described, and the form of apparatus forcarrying this method into effect, constitute preferred embodiments ofthis invention, it is to be understood that the invention is not limitedto this precise method and form of apparatus, and that changes may bemade in either without departing from the scope of the inventions, whichis defined in the appended claims.

1. A zone control exhaust terminal comprising: a housing having a firstopening coupled to a duct or open to a shaft and a second openingassociated with an area to be ventilated, said housing directing airflowfrom an inlet associated with said area to be ventilated along apredetermined path to an outlet; a damper hingeably coupled to saidhousing for controlling airflow between said area and a fan orventilator; a motor for driving said damper from a closed position atwhich said damper becomes situated in said predetermined path and anopen position at which said damper permits airflow from said inlet,along said predetermined path, and to said outlet in response to a motorcontrol signal in order to ventilate said area to be ventilated; and anairflow regulator situated in said predetermined path, said airflowregulator regulating airflow along said predetermined path from saidinlet to said outlet at a first predetermined, non-zero constant ratewhen said damper is in said closed position in order to ventilate airaway from said area to be ventilated by directing air away from saidarea to be ventilated as said airflow is regulated by said airflowregulator; said airflow regulator regulating said airflow passingtherethrough at said first predetermined, non-zero constant rate bypassively responding to dynamic fluctuations in duct pressure; wherein,when said damper is in said closed position, said airflow passes througha portion of a cross-sectional area of said housing containing saiddamper at said first predetermined, non-zero constant rate, and whensaid damper is in said open position, said airflow passes through saidcross-sectional area of said housing at a second, higher airflow rate;and wherein said airflow regulator is situated in at least one of: (i)said damper or (ii) said duct, which is located downstream of saiddamper.
 2. The zone control exhaust terminal as recited in claim 1wherein said airflow regulator is a dynamic constant airflow regulatorover a varying range of pressure.
 3. The zone control exhaust terminalas recited in claim 1 wherein said airflow regulator is integral withsaid damper.
 4. The zone control exhaust terminal as recited in claim 3wherein said damper is generally planar and pivots about a pivot axis,said airflow regulator being coupled to said damper such that it pivotsabout said pivot axis when said damper is actuated between said closedposition and said open position.
 5. The zone control exhaust terminal asrecited in claim 3 wherein said damper is generally planar and lies in afirst plane when said damper is in said closed position, said airflowregulator being coupled to said damper such that it also lies in saidfirst plane and permits airflow through said damper at said first rate.6. The zone control exhaust terminal as recited in claim 1 wherein saidairflow regulator is situated in said duct.
 7. The zone control exhaustterminal as recited in claim 1 wherein said airflow regulator issituated in said predetermined path when said damper is in said closedposition and removed from said predetermined path when said motoractuates said damper to said open position.
 8. The zone control exhaustterminal as recited in claim 1 wherein said airflow regulator permits aminimum amount of airflow from said area.
 9. The zone control exhaustterminal as recited in claim 8 wherein said minimum amount of airflow isat least 10 CFM.
 10. The zone control exhaust terminal as recited inclaim 1 wherein said motor control signal is generated by at least oneswitch.
 11. The zone control exhaust terminal as recited in claim 10wherein said switch responds to at least one of a humidity sensor,manual control, timed mechanism, occupancy, or other indicators ofpresence.
 12. The zone control exhaust terminal as recited in claim 1wherein said terminal further comprises a damper switch coupled to aremote fan for causing airflow in said duct, said damper switch beingactuated when said damper is moved to said open position.
 13. The zonecontrol exhaust terminal as recited in claim 12 wherein said damperactuates said damper switch in response to said motor driving saiddamper to said open position.
 14. The zone control exhaust terminal asrecited in claim 1 wherein said damper further comprises a pivot armcoupled to said motor and a spring mounted on said pivot arm for biasingsaid damper to said closed position.
 15. The zone control exhaustterminal as recited in claim 1 wherein said housing is dimensioned sothat it can be mounted between joists.
 16. The zone control exhaustterminal as recited in claim 1 wherein said damper, motor and airregulator may be detachably secured to said housing for maintenancewithout disconnecting said housing from said duct.
 17. The zone controlexhaust terminal as recited in claim 1 wherein said terminal furthercomprises a duct extension coupled to said housing in fluidcommunication with said first opening; said constant airflow regulatorbeing situated in said duct extension.
 18. The zone control exhaustterminal as recited in claim 17 wherein said terminal further comprises:a fan switch mounted for generating a fan signal when said damper isactuated to said open position.
 19. The zone control exhaust terminal asrecited in claim 17 wherein said terminal further comprises: a fanswitch mounted on a support; said fan switch being actuated by saiddamper when said damper is actuated to said open position.
 20. The zonecontrol exhaust terminal as recited in claim 1 wherein said terminalfurther comprises: a duct extension coupled to said housing in fluidcommunication with said first opening; and a second constant airflowregulator situated in said duct extension.
 21. A zone control exhaustterminal comprising: a housing having a first opening coupled to a ductor open to a shaft and a second opening associated with an area to beventilated, said housing directing airflow from an inlet to an outletalong a predetermined path; a damper hingeably coupled to said housingfor controlling airflow between said area and a fan or ventilator; amotor for driving said damper between a closed position at which saiddamper becomes situated in said predetermined path and an open positionat which said damper permits airflow along said predetermined path inresponse to a motor control signal; and an airflow regulator situated insaid predetermined path, said airflow regulator regulating airflow alongsaid predetermined path at a first rate when said damper is in saidclosed position; wherein said airflow regulator is integral with saiddamper; wherein said damper is generally planar and lies in a firstplane when said damper is in said closed position, said airflowregulator being coupled to said damper such that it also lies in saidfirst plane and permits airflow through said damper at said first rate;wherein said airflow regulator is a passively controlled constantairflow regulator over a varying pressure ranging between 0.20 and 0.80inches W.G.
 22. A zone control exhaust terminal comprising: a housinghaving a first opening coupled to a duct or open to a shaft and a secondopening associated with an area to be ventilated, said housing directingairflow from an inlet to an outlet along a predetermined path; a damperhingeably coupled to said housing for controlling airflow between saidarea and a fan or ventilator; a motor for driving said damper between aclosed position at which said damper becomes situated in saidpredetermined path and an open position at which said damper permitsairflow along said predetermined path in response to a motor controlsignal; and an airflow regulator situated in said predetermined path,said airflow regulator regulating airflow along said predetermined pathat a first rate when said damper is in said closed position; whereinsaid airflow regulator is integral with said damper; wherein a secondairflow regulator is situated in said duct; and wherein both saidairflow regulator and said second airflow regulator are passivelyresponsive to dynamic fluctuations in duct pressure.
 23. The zonecontrol exhaust terminal as recited in claim 22 wherein said airflowregulator permits a minimum amount of airflow from said area throughsaid duct and said second airflow regulator permits a maximum amount ofairflow from said area.
 24. The zone control exhaust terminal as recitedin claim 23 wherein said minimum amount of airflow is at least 10 CFMand said maximum amount of airflow is less than 400 CFM.
 25. A zonecontrol ventilation system for use in a building having a plurality ofareas to be ventilated, said system comprising: at least one fan unitfor generating airflow; a plurality of ducts coupled to said at leastone fan unit; a plurality of zone control exhaust terminals coupled toeach of said plurality of ducts, respectively, and operativelyassociated with each of said plurality of areas; each of said pluralityof zone control exhaust terminals comprising: a housing having an outletcoupled to at least one of said plurality of ducts and an inletassociated with at least one of said plurality of areas to beventilated; a damper pivotally coupled to said housing; a motor fordriving said damper between a closed position and an open position atwhich said damper permits airflow between said at least one fan unit andsaid at least one plurality of areas and into said at least one of saidplurality of areas to be ventilated in response to a motor controlsignal; and an airflow regulator situated in an airflow path, saidairflow regulator for regulating an airflow rate along said airflow pathbetween said at least one fan unit and said at least one of saidplurality of areas in order to ventilate said area by directing air awayfrom said area as said airflow is regulated when said damper is in saidclosed position; said airflow regulator regulating said airflow passingtherethrough at a first predetermined, non-zero constant rate bypassively responding to dynamic fluctuations in duct pressure; wherein,when said damper is in said closed position, said airflow passes througha portion of a cross-sectional area of said housing containing saiddamper at said first predetermined, non-zero constant rate, and whensaid damper is in said open position, said airflow passes through saidcross-sectional area of said housing at a second, higher airflow rate;and wherein said airflow regulator is situated in at least one of: (i)said damper or (ii) said at least one of said plurality of ducts, whichis located downstream of said damper.
 26. The zone control ventilationsystem as recited in claim 25 wherein said airflow regulator is anintegral dynamic constant airflow regulator.
 27. The zone controlventilation system as recited in claim 25 wherein said airflow regulatoris situated in an interior area of said damper.
 28. The zone controlventilation system as recited in claim 27 wherein said damper isgenerally planar and pivots about a pivot axis, said airflow regulatorbeing coupled to said damper such that it pivots about said pivot axiswhen said damper is actuated between said closed position and said openposition.
 29. The zone control ventilation system as recited in claim 27wherein said damper is generally planar and lies in a first plane, saidairflow regulator being coupled to said damper such that it lies in saidfirst plane, wherein said damper is in said closed position such that itpermits airflow at a minimum rate through said damper.
 30. The zonecontrol ventilation system as recited in claim 25 wherein said airflowregulator is situated in said duct.
 31. The zone control ventilationsystem as recited in claim 25 wherein said airflow regulator is removedfrom said predetermined path to permit airflow at a demand rate whensaid motor drives said damper to said open position in response to saidmotor control signal.
 32. The zone control ventilation system as recitedin claim 25 wherein said airflow regulator permits a minimum amount ofairflow.
 33. The zone control ventilation system as recited in claim 32wherein said minimum amount of airflow is at least 10 CFM.
 34. The zonecontrol ventilation system as recited in claim 25 wherein said motorcontrol signal is generated by at least one of a switch.
 35. The zonecontrol ventilation system as recited in claim 34 wherein said switchresponds to at least one of a humidity sensor, manual control, timedmechanism, occupancy, or other indicators of presence.
 36. The zonecontrol ventilation system as recited in claim 25 wherein said systemfurther comprises a switch coupled to said at least one fan unit forcausing airflow in said duct, said switch being actuated when saiddamper is driven from said closed position to said open position. 37.The zone control ventilation system as recited in claim 36 wherein saidswitch is a damper switch and said damper actuates said damper switch inresponse to said motor driving said damper to said open position. 38.The zone control ventilation system as recited in claim 25 wherein saiddamper further comprises: a pivot arm coupled to said motor; and aspring mounted on said pivot arm for biasing said damper to said closedposition.
 39. The zone control ventilation system as recited in claim 25wherein said at least one fan unit comprises an exhaust fan forgenerating an exhaust ventilation from each of said plurality of areas.40. A zone control ventilation system for use in a building having aplurality of areas to be ventilated, said zone control exhaust systemcomprising: at least one fan unit for generating airflow; a plurality ofducts coupled to said at least one fan unit; a plurality of zone controlexhaust terminals coupled to each of said plurality of ducts,respectively, and operatively associated with each of said plurality ofareas; each of said plurality of zone control exhaust terminalscomprising: a housing having an outlet coupled to at least one of saidplurality of ducts and an inlet associated with at least one of saidplurality of areas to be ventilated; a damper pivotally coupled to saidhousing; a motor for driving said damper between a closed position andan open position at which said damper permits airflow between said atleast one fan unit and said at least one plurality of areas and intosaid at least one of said plurality of areas to be ventilated inresponse to a motor control signal; and an airflow regulator situated inan airflow path, said airflow regulator for regulating an airflow ratealong said airflow path between said at least one fan unit and said atleast one of said plurality of areas; wherein said airflow regulator issituated in an interior area of said damper; wherein said damper isgenerally planar and lies in a first plane, said airflow regulator beingcoupled to said damper such that it lies in said first plane, whereinsaid damper is in said closed position such that it permits airflow atsaid airflow rate through said damper; wherein said airflow regulator isa passive dynamic constant airflow regulator.
 41. A zone controlventilation system for use in a building having a plurality of areas tobe ventilated, said system comprising: at least one fan unit forgenerating airflow; a plurality of ducts coupled to said at least onefan unit; a plurality of zone control exhaust terminals coupled to eachof said plurality of ducts, respectively, and operatively associatedwith each of said plurality of areas to be ventilated; each of saidplurality of zone control exhaust terminals comprising: a housing havingan outlet coupled to at least one of said plurality of ducts and aninlet associated with at least one of said plurality of areas to beventilated; a damper pivotally coupled to said housing; a motor fordriving said damper between a closed position and an open position atwhich said damper permits airflow between said at least one fan unit andsaid at least one plurality of areas and into said at least one of saidplurality of areas to be ventilated in response to a motor controlsignal; and an airflow regulator situated in an airflow path, saidairflow regulator for regulating an airflow rate along said airflow pathbetween said at least one fan unit and said at least one of saidplurality of areas; wherein said airflow regulator is situated in aninterior area of said damper; wherein a second airflow regulator issituated in said at least one of said plurality of ducts to regulateairflow at a maximum airflow rate.
 42. The zone control ventilationsystem as recited in claim 41 wherein said airflow regulator permits aminimum amount of airflow and said second airflow regulator permits saidmaximum amount of airflow.
 43. The zone control ventilation system asrecited in claim 42 wherein said minimum amount of airflow is at least10 CFM and said maximum amount of airflow is less than or equal to 400CFM.
 44. A system for regulating airflow in a structure having aplurality of zones; said system comprising: an airflow generator; aplurality of terminals associated with each of said plurality of zones,respectively; a conduit for coupling said airflow generator to each ofsaid plurality of terminals; said plurality of terminals comprising aplurality of primary regulators in the form of pivotable dampers,respectively, for causing airflow to a demand level in at least one ofsaid plurality of zones in response to a demand; a plurality of firstconstant airflow regulators situated between each of said plurality ofzones, respectively, and said airflow generator to regulate airflow to afirst predetermined level between said airflow generator and those otherplurality of zones where demand airflow to said demand level is notdemanded; and a plurality of second constant airflow regulators situatedin said conduit for regulating airflow to a second predetermined level;wherein both said plurality of first constant airflow regulators andsaid plurality of second constant airflow regulators are passivelyresponsive to dynamic fluctuations in duct pressure.
 45. The system asrecited in claim 44 wherein each said damper of each of said pluralityof primary regulators has an aperture therein for receiving one of saidplurality of first constant airflow regulators so that airflow in saidother plurality of zones where demand airflow is not demanded is lessthan or equal to said first predetermined level.
 46. The system asrecited in claim 44 wherein each of said plurality of first constantairflow regulators is coupled to said primary regulator.
 47. A systemfor regulating airflow in a structure having a plurality of zones: saidsystem comprising: an airflow generator; a plurality of terminalsassociated with each of said plurality of zones, respectively; aplurality of conduits for coupling said airflow generator to each ofsaid plurality of terminals; a plurality of primary regulators coupledto said plurality of terminals, respectively, for causing airflow to ademand airflow level in one of said plurality of zones in response to ademand; a plurality of first constant airflow regulators situatedbetween each of said plurality of zones, respectively, and said airflowgenerator to regulate airflow between said airflow generator and thoseother plurality of zones where demand airflow to said demand airflowlevel is not demanded, wherein each of said plurality of first constantairflow regulators regulates airflow to a first predetermined airflowlevel; and a plurality of second constant airflow regulators situated insaid plurality of conduits, respectively, between each of said pluralityzones and said airflow generator to regulate airflow to each of saidplurality of conduits to a second predetermined airflow level.
 48. Asystem for regulating airflow in a structure having a plurality ofzones: said system comprising: an airflow generator; a plurality ofterminals associated with each of said plurality of zones, respectively;a conduit for coupling said airflow generator to each of said pluralityof terminals; a plurality of primary regulators coupled to saidplurality of terminals, respectively, for causing airflow to a demandairflow level in one of said plurality of zones in response to a demand;a plurality of first constant airflow regulators situated between eachof said plurality of zones, respectively, and said airflow generator toregulate airflow between said airflow generator and those otherplurality of zones where demand airflow to said demand airflow level isnot demanded to a first predetermined airflow level, wherein saidconduit comprises a plurality of ducts coupling said airflow generatorto said plurality of zones, respectively; and a plurality of secondconstant airflow regulators situated in said plurality of ducts,respectively, between said plurality of terminals and said airflowgenerator, said plurality of second constant airflow regulatorsregulating airflow to a second predetermined airflow level when saidprimary regulator permits airflow to said demand airflow level.
 49. Thesystem as recited in claim 48 wherein said first predetermined airflowlevel is a minimum level and said second predetermined airflow level isa maximum level, said demand airflow level being greater than or equalto said minimum level, but less than or equal to said maximum level. 50.The system as recited in claim 48 wherein said airflow generatorgenerates airflow to a first airflow level and automatically generatesairflow to said demand airflow level in response to one of saidplurality of primary regulators causing airflow to said demand airflowlevel.